It is known that intervertebral discs are prone to injury and degeneration. For example, herniated discs are common, and typically occur when normal wear, or exceptional strain, causes a disc to rupture. Degenerative disc disease typically results from the normal aging process, in which the tissue gradually looses its natural water and elasticity, causing the degenerated disc to shrink and possibly rupture.
Intervertebral disc injuries and degeneration are frequently treated by replacing or augmenting the existing disc material. Current intervertebral disc implants tend to utilize synthetic materials, particularly hydrogels, to augment or replace the original disc. These synthetic materials are commonly covered with textured fabrics whose rough surfaces may accelerate wear of the encapsulated hydrogel or the bone endplates of the intervertebral body. Such wear may generate wear particles, and can cause adverse biological responses such as osteolysis in the vertebral body endplate bone and subsequent subsidence of the implant.
For example, reports on the use of prosthetic nucleus replacement devices with polyethylene mesh jackets have indicated subsidence of these devices into the endplates of the vertebral bodies. Subsidence is also due to the rigid compliance of the jacket and hard hydrogel core. This modulus mismatch with the vertebral bone, combined with the other design features mentioned above, contributes to implant subsidence.
To avoid the problems associated with synthetic materials, natural materials may be used to repair or augment intervertebral discs. For example, U.S. patent application Ser. No. 10/245,955, incorporated herein by reference, discloses the use of natural collagen-based materials to repair and/or augment intervertebral discs.
The use of natural collagen-based materials to repair and/or augment intervertebral discs finds particular utility when used to provide annular plugs and/or nucleus implants that have the characteristics of natural tissue yet remain securely in place.
In view of the above it can be seen that a need exists for improved annular plugs and/or nucleus implants made of natural collagen-based materials, and particularly of allogenic or xenogenic materials. The present invention addresses that need.